This invention relates to a material for sliding surface bearings, which material comprises a metallic backing having a thickness of 0.5 to 2.5 mm and consisting preferably of steel, bronze or a high-strength aluminum alloy, a porous substrate layer having a thickness of 0.2 to 0.4 mm and consisting of tin bronze, tin-lead bronze or an aluminum bearing alloy and applied to said backing, a mixture of polytetrafluorethylene (PTFE) and 15 to 25% by volume of a filler for improving the thermal conductivity and wear resistance and completely filling the pores of said substrate layer, and an antifriction layer having a substrate layer, and an antifriction layer having a thickness of 0.01 to 0.03 mm and consisting of the PTFE-filler mixture and provided on said substrate layer.
Such a composite described, e.g., in VDI-Z. 110 (1968), No. 15, pages 632-636, permits a full utilization of the special properties of PTFE, namely, low coefficient of friction, nonaggressive behaviour, high thermostability from -200.degree. to +280.degree. C. and high chemical stability, whereas its less desirable properties do not affect the properties of the bearing. PTFE has a relatively low strength, a high thermal expansion and a low thermal conductivity. These disadvantages are rendered ineffective by the metallic backing and the sinter-bonded porous substrate. Owing to the presence of the backing and of the substrate layer, the material for sliding surface bearings has a compressive strength of 360 N/mm.sup.2 and in expansion behavior is similar to steel. The substrate layer lubricates the PTFE and ensures a high dissipation of heat from the bearing gap. The mixture of PTFE and lead acts like a permanent or solid lubricant. The material for sliding surface bearings can be used without any lubricant for pv values of 1.8 N/mm.sup.2 in continuous operation and, up to 3.6 N/mm.sup.2 in intermittent operation. When the above-mentioned pv capacities are fully utilized during a dry running of the bearing, a sliding speed of v=2 mm/sec. should not be exceeded. When the bearing has been completely run in, the wear to a depth of about 0.04 to 0.05 mm is proportional to the pv value so that the life of the material for sliding surface bearings will be inversely proportional to the pv factor.
Owing to the properties described hereinbefore, the material for sliding surface bearings can be used for a multitude of purposes. For instance, in mechanical engineering, it is no longer required in many cases to provide conventional lubricating systems, which are often highly expensive. The dry running of the bearings improves their safety in operation because there is no need for a servicing by a supply of additional lubricant. But a disadvantage resides in the fact that the bearing elements made from that maintenance-free material for sliding surface bearings cannot be used in a lubricant-containing environment, e.g., in shock absorbers, hydraulic pumps or the like, where they are subjected to alternating loads so that the bearing surface and the surface in contact therewith are often separated from each other; because under such conditions the lubricants effect an erosion of the PTFE-lead mixture as a result of cavitation.